The present invention pertains to both a high power lighting product comprising a plurality of light emitting diodes (LEDs) and an arrangement for removing heat from the lamp.
High power LED illumination sources are replacing incandescent bulbs in many applications for reasons including cost savings from longer service life. Many such LED lamps are made from an array of blue-light emitting GaN LEDs combined with a phosphor that converts a fraction of the blue light to yellow light which, when mixed with the blue light, provides an acceptable replacement for a white incandescent source. Both the LED and the phosphor components in such a light source become less efficient when the temperature rises above ninety to one hundred degrees Celsius. In order to remove heat from the active lamp components, some prior art LED lamps have used a chip-on-board (COB) construction approach in which each LED is bonded to a ceramic-coated metal substrate that conducts heat away from the active device.
A filament of an incandescent bulb is very small in comparison to the rest of the bulb and to whatever reflecting or refracting optical elements are used to control the directional output of the light. Thus, an incandescent bulb provides a reasonable approximation of an ideal point source of light, which is desirable if the light from the source is to be focused. When simulating an incandescent source with an LED array, the LEDs are commonly set close together in a planar array that mimics the incandescent filament, but that is necessarily somewhat larger. This relative close packing of the LEDs can lead to overheating even if one uses a substrate with a high thermal conductivity.
In many lighting applications one desires a relatively diffuse source of illumination, such as one finds in ceiling fixtures in which light from a fluorescent or incandescent source is passed through a diffusing screen or globe of some sort.